1. Field of Invention
The present invention relates to a method for preparing a suspension. More particularly, the present invention relates to a method for processing a ceramic powder suspension.
2. Description of Related Art
Fine ceramics refer to ceramic materials that use highly refined powder ingredients and are precisely processed to provide the particular microstructure and exceptional functions. Functionally, these materials are more thermal resistant, more durable, etch-resisted than the conventional ceramic materials. Further, they also comprise optical, electrical and magnetic properties. The fine ceramics are thus widely used and is becoming a significant industrial material in the fixture.
As the particle size of ceramic powder reduces from a micrometer level to a sub-micron level or even to a nanometer level, particle agglomeration in a suspension becomes a serious issue. An effective dispersing agent thereby plays an important role in the processing of ceramic powder. For a barium titanate water based slurry, the current industry often uses Darvan C (PMAAN) as a dispersing agent. The chemical name of Darvan C (PMAAN) is ammonium polymethacrylate, which can provide a certain degree of dispersing effect. However, there is still room for improvement. When PMAAN is used as a dispersing agent for a barium titanate slurry, barium titanate in water reacts with hydrogen ions to dissociate barium ions, and the physicochemical property at the surface of barium titanate becomes similar to that of titanium dioxide. The dissociated barium ions are re-absorbed onto the surface of the powder. The ratio of barium to titanium of the powder not only changes, the thickness of a Ba-depleted, TiO2-rich surface layer of the powder also becomes greater due to the dissolution of the barium ions. The surface structure is thereby less dense and an abnormal grain growth is resulted during sintering. The quality of the product is adversely affected.